Apparatus and method for optically detecting the emissions of a plasma produced in a conductive liquid by means of electrodes with different areas in contact with the liquid

An apparatus comprises: a chamber (100) configured to be filled with electrically conductive liquid (102); a first electrode (104) and a second electrode (106) located within the chamber (100); an optical radiation receiver (126); and an electrically conductive contact area (108) of the first electrode (104) and an electrically conductive contact area (110) of the second electrode (106) are configured to be in contact with the liquid (102) of the chamber (100) wherein the electrically conductive contact area (108) of the first electrode (104) is configured to be smaller than the electrically conductive contact area (110) of the second electrode (106). The first electrode (104) and the second electrode (106) are configured to receive electric energy and output the electric energy to the liquid (102) in order to cause substance of the liquid (102) to emit optical radiation at the electrically conductive contact area (108) of the first electrode (104) on the basis of densification of the electric energy due to the smaller electrically conductive contact area (108) of the first electrode (104). The optical radiation receiver (126) is configured to receive the optical radiation for analysis of the liquid (102).